Counterpressure steam systems can be power units in which the combustion heat, i.e. the heat generated by combustion of a fuel, or the heat from some other external source, can be used to cover the power requirements and the thermal requirements of the system.
Water vapor at high pressure and high temperature is generated in a boiler and is used to drive a high-pressure turbine in which the steam is expanded to a certain temperature level and/or pressure. The conventional systems, moreover, permit steam to be recovered at the output for expansion in another turbine in a second stage and/or to cover thermal requirements of the plant. An apparatus of this type is described, for example, in Linde Berichte aus Technik und Wissenschaft, 38, 1976, pages 3-8 (Linde Reports of Technology and Science).
In power-intensive industries, the requirements for electrical and mechanical energy cannot always be covered by such types of apparatus. For example, this is the case in olefin and ammonia plants as described in the above-mentioned article. It is usually necessary with such systems to introduce additional electrical energy, in the form of current supplied from the exterior or outside the plant or installation, or to generate mechanical energy with other fuels to satisfy the requirements of the plant or installation. With the present high cost of energy, this need for external sources has posed a significant problem, especially since the internal plant energy is frequently not fully utilized or economically exploited.